The baboon as a model for immunological studies of Schistosoma mansoni infections will be further characterized. Fate of worms relative to immunity development will be determined. The hypothesis of an immune mechanism basis for acquired immunity in primates will be tested by an immunosuppression experiment in rhesus monkeys. ALG and chemical immunosuppressants will be used in combined therapy in an effort to abrogate immunity. The hypothesis of concomitant immunity will be tested in rhesus monkeys by surgically implanting marked (multilated or sexed) worms, which will be distinguishable from worms maturing from a challenge infection. The hypothesis of reaginic antibody protective immunity will be tested in baboons which, after passive intradermal transfer of baboon IgG anti-schistosome reagins, will be percutaneously challenged through the skin injection site.